Pen design



FIG. 1 is a left side view of a pen design showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a front view thereof; and,

FIG. 6 is a rear view thereof. 

The ornamental design for a pen design, as shown and described. 